1. Field of the Invention
The present invention relates to a method for manufacturing a coated body of, for example, a core for a small-sized motor.
2. Prior Art
A small-sized motor having a core are useful in domestic electrical appliances, automobile electrical instrumentations, AV (audio-visual)units, electrical communication and others.
The core, as shown in FIG. 1, has a plurality of multi-polar radial thin plates 3 having a shaft hole 1 and poles (slots) 2 formed from, for instance, thin metal sheets of 0.35 mm laminated through compression, and as shown in FIG. 2, an insulation coat film 4 is applied on a laminated body of multi-polar radial thin plates 3. Wire coated with insulation (not shown) is wound on the laminated body of respective slots through the insulation coat film 4.
The thin metal sheet used in the manufacturing process mentioned above, is initially formed by a press, resulting in the formation of burrs at its cut edges. These multi-polar radial thin plates 5 having burrs 5a are laminated and integrated as shown in FIG. 3, and the insulation coat film 4 as shown in FIG. 2 is formed (not shown) . Then, when the wire is wound, the winding force destroys the insulation coat film 4 on the burrs and the insulation film on the wires also exfoliate resulting in the reduction of the breakdown voltage between the wound wire and the core. The sharp points of these burrs are typically removed by laser cutting or blast; however, the edge of the laminated body of the multipolar radial thin plates 5 may also destroy the insulation coat film 4 by the winding force when the wire is wound resulting in the breakdown voltage reduction.
When the film thickness is at most about 20 .mu.m, such as formed in electro deposition, the film does not extend beyond the burrs. Alternatively, electrostatic fluidized bed powder coating provides a thick film coating of 200 to 300 .mu.m which affords great reliability for edge insulation. However, a thick coat film is inappropriate for small cores of several millimeters in diameter since the space between the slots is reduced limiting the number of windings and inhibiting the ability to obtain a high torque. Also the excessive winding length increases the heat generation by the increased resistance for cores of 10 mm in diameter for example. Therefore electrostatic powder coating methods are preferable because it allows the formation of the insulation coat film 4 of about 40 to 100 .mu.m. In particular, the friction charged type electrostatic powder coating method or the inner charged type electrostatic powder coating method allow coating of the bottom of cavities of an electric member ensuring the desired film thickness of about 40 to 100 .mu.m. This improves the edge cover rate, that is, the value obtained by multiplying by 100 the ratio y/x of the coat thickness y of the edge portion to the coat thickness x of the flat portion of the insulation coat film 4 shown in FIG. 2 as disclosed in Tokuganhei JP App. No. 7-221157, filed Aug. 8, 1995.
However, in this electrostatic powder coating method, as shown in FIG. 4, a shaft 6a composed of magnet is introduced into one of the sides of the shaft hole 1a of a core made of a laminated body of multipolar radial thin plates 3. While a shaft 6b made of iron is introduced into the other side, the core is supported and rotated by a jig composed of shafts 6a and 6b inserted into the respective collars 6a-1 and 6b-1, which are contacted to the periphery of this shaft hole 1a and coated by a coating gun. Therefore, the portions covered by the jig 6 and not powder coated, namely the inner wall of the shaft hole 1a and the portion around the both end faces thereof covered by the collars 6a-1 and 6b-1 can not be coated. Moreover, after the powder coating, the powder coat applied to the outer circumferential surface 3a-1 of the core 3a may detach before its baking resulting in an uncoated exposed portion.
Thus, if some portions remain uncoated, not only does rust eat these portions, but also moisture may enter from these portions into the gap between the multipolar radial thin plates 3 of the laminated body and rust may eat these multipolar radial thin plates.
When rust eats precise electronic devices that are recently coming into use, their long term reliability deteriorates.
Particularly, as the small-sized motor for the driving section of computer itself, hard disk, optical magnetic disk or other peripheral devices for the OA (office automation) unit, the FA (factory automation) unit or the like comes into wide use, it becomes all the more important to prevent rust from eating the core to ensure the motor reliability.
The first object of the present invention is to provide a method for manufacturing a coated body of metal member for electronic components having a coating film of the thickness that would not be destroyed even when the metal member for electronic components has burrs.
The second object of the present invention is to provide a method for manufacturing a coated body of metal member for electronic components having a coat film on a portion covered by a jig, which by previously known methods was unable to be coated.
The third object of the present invention is to improve the reliability of a small-sized motor that can keep a high torque for a long period of time to be used for computer related electronic devices.
The fourth object of the present invention is to provide a method for manufacturing a coated body that would not reduce the edge cover ratio of metal member for electronic components consisting of a thin, for example 100 .mu.m or less, insulation coat film for a small electrical member having cavities.
The fifth object of the present invention is to provide a method for manufacturing a coated body of a metal member for electronic components having an insulation coat film that does not shorten the number of windings of the motor core thereby reducing its electric resistance and limiting its heat generation.